Images that are captured using a camera generally have several kinds of color problems. For example, if the camera is not properly white balanced, images tend to have a red or blue cast. If there is insufficient lighting in the scene, images tend to be dark and show little contrast. Also, if light reflects off objects in the scene, other objects tend to have a color cast associated with the reflected light.
These and other color problems commonly are fixed using color correction tools on a computer workstation. These tools allow a user to select one or more image processing functions to apply to an image and to adjust parameters of these functions. Currently available color correction tools are powerful, but tend to have a steep learning curve.
To reduce the learning curve and the time required to manipulate the image processing functions, there are some automatic tools for color correction. Such tools analyze an image and adjust parameters of a color correction operation to improve the color in the image. An example of such a tool is the PHOTOSHOP software from Adobe Systems Incorporated of Menlo Park, Calif. An example kind of function that may be provided is automatic color balancing. Using automatic color balancing, a histogram of the red, blue and green channels is created. The histogram is then stretched so that it matches the end points of the range of values for each channel or the minimum and maximum values from among the red, green and blue channels. Such automatic color balancing generally also improves the contrast of the image, which is generally desirable.
However, color correction for video, which is a sequence of images, is more complicated. Although it may be possible to analyze and correct separately every image in a sequence of images, such analysis and correction would consume significant processing resources. On the other hand, it may be undesirable to apply contrast modifications developed by analysis of one image to other images. A change in contrast in one image may not be appropriate to apply to another image. Also, the change in contrast to the other image may negatively impact its quality.